WASHINGTON (CNN) -- The United States has new intelligence indicating Iran is reorganizing in an effort to assert its influence inside Iraq and may be behind several recent attacks, according to a senior U.S. official who spoke with CNN Monday.

An Iraqi soldier outside in Dora district, Baghdad, Iraq, on Tuesday.

The information underscores a view by Gen. David Petraeus, who assumes command of U.S. Central Command later this month, and Gen. Raymond Odierno that progress in Iraq remains fragile and that it is too soon for a major additional U.S. troop drawdown.

The senior official, who asked to remain anonymous because of the sensitivity of the intelligence, said the U.S. military had recently arrested an Iraqi general who says he was paid by Iran to derail a pending agreement that would allow U.S. troops to remain in Iraq after the end of the year.

The general was arrested a few weeks ago at the Iranian border carrying large sums of cash, according to the source. The man has known ties to the Iranian Revolutionary Guard Corps (IRGC), the U.S. official said.

The United States believes the IRGC has ties to terrorist operations and Iran's programs to develop chemical and biological weapons.

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Odierno, who took over for Petraeus as the top U.S. military official in Iraq, told the Washington Post on Sunday that intelligence reports indicated Iran was bribing Iraqi officials in an attempt to undermine the status-of-forces agreement between the United States and Iraq.

But, the general said, he had no proof of the bribes.

The senior official described overall Iranian efforts as a "reorganization" rather than a "resurgence." As a result of the U.S. troop surge, many Iranian-backed fighters in Iraq fled back across the border. U.S. intelligence believes some fighters may have come back into Iraq, but most are still in Iran.

According to the latest assessment of U.S. intelligence, the Iranian effort has broken into three main groups: Asaib-al-haq; Khataib Hezbollah; and a reorganized so-called "special groups" effort, the official said.

He noted that the first two groups represent fighters are coordinated by Iranian elements, instead of Iraqi cleric Muqtada al Sadr's group, which formerly controlled them.

"They are now directly funded and trained by the IRGC," the U.S. official said. It is believed the IRGC is trying to model this effort after Hezbollah in Lebanon, he said.

That view would suggest the Iranians will try to exert their influence through social outreach organizations, such as providing schools, health care and other services in Iraq.

All three groups "have changed tactics and are primarily focused on assassinations and kidnappings," along with targeted bomb attacks, rather than the large-scale attacks against Iraqi civilians seen in the past, the official said.